U.S. Pat. No. 3,815,410 describes a thermodynamic cycle analyzer for internal combustion engines, using a volume signal generator attached to the crankshaft of the engine. The analyzer of U.S. Pat. No. 3,815,410 produces the volume signal by rotating an eccentric disc between a radially positioned elongated light source (i.e., evenly illuminated slot) and a photocell. The length of the light source seen by the photocell is thus made a function of the angular position of the eccentric disc, which in turn is a function of the piston position and therefore the volume of the combustion chamber.
The problems with the arrangement of U.S. Pat. No. 3,815,410 is that when the device is used on fastrunning engines, the eccentric weight distribution of the disc sets up vibrations which impair the accuracy of the photoelectric arrangement beyond permissible limits.